Radio frequency identification (RFID) circuitry has been used to detect the presence and movement of articles of interest. The presence of an article bearing an RFID tag may be electronically detected by wirelessly interrogating the RFID tag, either intermittently or continuously. In a typical application, the RFID tag stores an identification (ID) code. When interrogated by an RFID tag reader, the RFID tag wirelessly transmits its ID code to the RFID tag reader. The code transmitted by the RFID tag to the RFID tag reader indicates the presence and identification of the article bearing the RFID tag.
RFID tags may include a battery or other independent power source, or they may acquire their power from the signal transmitted by the external RFID tag reader. RFID tags without independent power are particularly small and inexpensive, making them very cost effective for tracking a large number of objects.
A technology related to RFID involves electronic article surveillance (EAS) tags. Both EAS and RFID tags are remotely accessible, but EAS tags typically do not include the data storage capabilities of RFID. Both EAS and RFID tags include a transponder circuit for remote access. The transponder circuit is a resonant circuit having components selected and arranged so that the transponder electrically resonates at a particular frequency.
If an electromagnetic signal at or near the transponder resonant frequency is emitted from a tag reader within range of the EAS tag, the EAS transponder circuit absorbs and/or reflects energy from the electromagnetic field emitted by the reader through inductive coupling. The energy absorbed or reflected by the transponder circuit can produce a change in the output signal of the tag reader output coil or in the input signal at the tag reader receiving coil. These signal changes may be interpreted to indicate the presence of an EAS tagged article.
In some applications, it is desirable to remotely acquire sensor information. The remote access capabilities of RFID and EAS tags may be combined with sensor technology to provide remote sensing capability. The present invention fulfills these and other needs, and offers other advantages over the prior art.